This project was initiated to identify those polypeptides that specifically relate to the metastatic process as the first step toward their purification and identification. Utilization of metastasizing and non-metastasizing cells derived from the same parent population of tumor cells is fundamental to this project, and we have confirmed that the TMT-081-ms cells do metastasize in syngeneic rats and that the TMT-081-nm do not metastasize in syngeneic rats. Radiolabelling of these cells with 14C amino acids has revealed several qualitative and quantitative differences in their polypeptide patterns. The most intensely labelled spots that occurred only in the metastatic cells were (MW/pI) 67/5.5 and 50/4.5 and the most intense spots occurring only in the non-metastatic cells were 46/6.7 and 38/6.1. When 32P was used to radiolabel these cells, the resultant polypeptide patterns were markedly different from those obtained with 14C amino acid labelling. A number of the 32P-labeled polypeptides could not be observed on the 14C autoradiograms. There were again several qualitative and quantitative differences that could be observed from visual inspection of the autoradiograms between the metastatic and non-metastatic cells lines. The most intensely labelled spots occurring only in the metastatic cells were 98/4.7 and 24/4.5. Those polypeptides that were approximately threefold greater in intensity in the metastatic cells compared to the non-metastatic were 14/5.2, 15/5.4 and 12/6.3. The polypeptides of 40/5.9 and 40/5.8 were at least threefold greater in the intensity of 32P label compared to the corresponding polypeptides in the metastatic cells.